1. Field of the Invention
The present invention relates to new crystalline metal silicate and metal borosilicate compositions. This invention particularly relates to a method of preparing these compositions and to certain catalytic conversion processes employing these compositions.
2. Description of the Prior Art
Zeolitic materials, both natural and synthetic, are known to have catalytic capability for various types of reactions, especially hydrocarbon conversions. The well-known crystalline aluminosilicate zeolites are commonly referred to as "molecular sieves" and are characterized by their highly ordered crystalline structure and uniformly dimensioned pores, and are distinguishable from each other on the basis of composition, crystal structure, adsorption properties and the like. The term "molecular sieves" is derived from the ability of the zeolite materials to selectively adsorb molecules on the basis of their size and form.
The processes for producing such crystalline synthetic zeolites are well known in the art. A family of crystalline aluminosilicate zeolites, designated ZSM-5, is disclosed in U.S. Pat. No. 3,702,886, said patent being incorporated herein by reference. The family of ZSM-5 compositions has a characteristic X-ray diffraction pattern and, can also be identified, in terms of mole ratios of oxides, as follows: EQU 0.9.+-.0.2M.sub.2/n O:W.sub.2 O.sub.3 :5-100YO.sub.2 :zH.sub.2 O
wherein M is a cation, n is the valence of said cation, W is selected from the group consisting of aluminum and gallium, Y is selected from the group consisting of silicon and germanium, and z is from 0 to 40. In a preferred synthesized form, the zeolite has a formula, in terms of mole ratios of oxides, as follows: EQU 0.9.+-.0.2M.sub.2/n O:Al.sub.2 O.sub.3 :5-100SiO.sub.2 :zH.sub.2 O
and M is selected from the group consisting of a mixture of alkali metal cations, especially sodium, and tetraalkylammonium cations, the alkyl groups of which preferably contain 2-5 carbon atoms.
U.S. Pat. No. 3,941,871 relates to novel crystalline metal organosilicates which are essentially free of Group IIIA metals, i.e., aluminum and/or gallium. This patent is incorporated herein by reference. It is noted therein that the amount of alumina present in the known zeolites appears directly related to the acidity characteristics of the resultant product and that a low alumina content has been recognized as being advantageous in attaining a low degree of acidity which in many catalytic reactions is translated into low coke making properties and low aging rates. A typical procedure for making the organosilicates is to react a mixture containing a tetraalkylammonium compound, sodium hydroxide, an oxide of a metal other than a metal of Group IIIA, an oxide of silicon, and water until crystals of said metal organosilicates are formed. It is also noted in the patent that the family of crystalline metal organosilicates have a definite X-ray diffraction pattern which is similar to that for the ZSM-5 zeolites. Minor amounts of alumina are contemplated in the patent and are attributable primarily to the presence of aluminum impurities in the reactants and/or equipment employed.
U.S. Pat. No. 3,844,835 discloses crystalline silica compositions. The crystalline silica materials may also contain a metal promoter which may be selected from Group IIIA, Group VB or Group VIB elements.
U.S. Pat. No. 4,088,605 is directed to the synthesis of a zeolite, such as ZSM-5, which contains an outer shell free from aluminum. The patent states at column 10, line 20 at seq., that to produce the outer aluminum-free shell it is also essential that the reactive aluminum be removed from the reaction mixture. It is therefore necessary, as noted therein, to process the zeolite and to replace the crystallization medium with an aluminumfree mixture to obtain crystalization of SiO.sub.2 on the surface of the zeolite which can be accomplished by a total replacement of the reaction mixture or by complexing from the original reaction mixture any remaining aluminum ion with reagents such as gluconic acid or ethylenediaminetetraacetic acid (EDTA).
Crystalline borosilicate compositions are disclosed in German Offenlegungschrift No. 27 46 790. This application relates specifically to borosilicates which are prepared using the usual procedures for making the aluminosilicate zeolites. It is noted therein that in instances where a deliberate effort is made to eliminate aluminum from the borosilicate crystal structure because of its adverse influence on particular conversion processes, the molar ratios of SiO.sub.2 /Al.sub.2 O.sub.3 can easily exceed 2000-3000 and that this ratio is generally only limited by the availability of aluminum-free raw materials.
German Offlenegungschrift No. 28 48 849 relates to crystalline aluminosilicates of the ZSM-5 zeolite series. These particular zeolites have a silica to alumina mole ratio greater than 20 and are prepared from a reaction mixture containing a source of silica, alumina, a quaternary alkyl ammonium compound and a metal compound including such Group VIII metals as ruthenium, palladium and platinum.
U.S. Pat. No. 4,113,658 relates to the precipitation of metal compounds on support materials and discloses the decomposition of urea to form ammonia which in turn causes the formation of precipitates of metal hydroxides which deposit on solid support materials. No suggestion is made of applying this technique to the preparation of crystalline zeolites.
While the art has provided zeolitic catalysts having a wide variety of catalytic and adsorptive properties, the need still exists for crystalline materials having different and/or enhanced catalytic properties. For example, an important use for a crystalline material is in conversion processes of oxygenated compounds such as the conversion of dimethyl ether and methanol to aliphatic compounds as well as the conversion of synthesis gas or hydrocarbons, such as ethylene, at a significant level of conversion and selectivity.
It is an object of this invention to provide novel crystalline metal silicate and metal borosilicate compositions.
It is another object of this invention to provide novel crystalline metal silicate and metal borosilicate compositions having different and enhanced catalytic properties.
It is a further object of this invention to provide a method of preparing novel crystalline metal silicate and metal borosilicate compositions from mixtures of appropriate oxides.
It is a still further object of this invention to provide an improved method for the conversion of hydrocarbons, synthesis gas or oxygenated organic compounds to useful end products at significant conversion rates and product selectivity.